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Do I need to run collision detection twice, one for rigid bodies, and again for non-rigid bodies?

JackOfCandles · 2021-08-03T08:11:06

Imagine the following scenario with three hitboxes, before the collision detection & resolution occurs: The green rectangle represents the player and is a rigid body. The blue rectangle represents a wall, and is also a rigid body. The red rectangle represents a collectible power-up, which disappears when the player picks it up and is not a rigid body. In this scenario, the player was to the left of the wall, is moving right, and collides with the wall. I've run into a problem where the order that the collision tests between the regions occurs is unpredictable and can result in incorrect behavior. If the player and the wall collision is resolved first, the player is correctly re-positioned to the left of the wall, and will no longer be colliding with the power-up. However, if the collision test with the power-up is done first, the player would collect it, which is not the correct behavior. Naturally, the scene could also be mirrored, with the power-up to the left of the wall and the player to the right, moving left. The only thing I can think of to deal with this problem is to do two passes for collection detection, one for collisions between rigid bodies only, and another for non-rigid bodies. This seems really inefficient though, so I'm wondering if there's a better way to address this. Any thoughts would be appreciated. Thanks!

General and Gameplay Programming Programming

Started by JackOfCandles July 25, 2021 04:23 AM

10 comments, last by JoeJ 3 years, 4 months ago

JoeJ

4,359

August 03, 2021 08:11 AM

hplus0603 said:
Yeah, but what do you think the physics engine is doing under the covers? ;-)

The main reason for me to use Newton is it really tries to follow laws of physics. So it does not use the mentioned tricks.
In contrast to all other engines i have tried, it has really minimal jitter and is very accurate. For example, i made a self balancing walking ragdoll, and its built in solver is accurate enough so this just works. Using other engines, i would need to make my own torque solver for the motorized joints.

Though, i did not look at other engines for >15 years. There were improvements on PhysX related to robotics since that, for example.